1. Technical Field
The present invention relates to a shock absorber including a damping-force generating device that controls a flow of working fluid caused by sliding of a piston in a cylinder and thereby generates a damping force.
2. Related Art
As a shock absorber used as a rear cushion that suspends a rear wheel of a motorcycle on a vehicle body, for example, there is a hydraulic shock absorber including a damping-force generating device that controls a flow of oil caused by sliding of a piston in a cylinder and thereby generates a damping force. Various techniques have been proposed concerning such a hydraulic shock absorber.
FIG. 11 is a longitudinal sectional view of a main part of a related-art shock absorber. As shown in FIG. 11, in a shock absorber 201, a part of a piston rod 203 is inserted from above into a cylinder 202 in which oil is sealed. A piston 204 is coupled to the lower end portion of the piston rod 203. The piston 204 is slidably fitted in the up-down direction on the inner circumference of the cylinder 202. An inside of the cylinder 202 is sectioned into a cylinder upper chamber S11 and a cylinder lower chamber S12 by the piston 204. A compression-side oil passage 205 and an extension-side oil passage 206 are formed in the piston 204. A main disk valve 207 that selectively opens and closes the compression-side oil passage 205 and a main disk valve 208 that selectively opens and closes the extension-side oil passage 206 are respectively formed on the upper and lower surfaces of the piston 204.
Flows of the oil caused in the compression-side oil passage 205, and the extension-side oil passage 206 by sliding of the piston 204 in the cylinder 202 are respectively controlled by the main disk valves 207 and 208, whereby a damping force is generated. The damping force is adjusted by controlling a valve opening pressure of the main disk valves 207 and 208. The valve opening pressure is controlled by an internal pressure of back pressure chambers 213 and 214 caused by a channel area difference between back pressure chamber inlet oil passages 211 and 212 respectively provided in valve members 209 and 210 and notch-like downstream side orifices 217 and 218 respectively formed in outer circumferences of relief valves 215 and 216.
FIG. 12 is a longitudinal sectional view of a damping force adjusting valve 310 connected to a related-art shock absorber 301 and a hydraulic circuit diagram of the entire shock absorber. In the shock absorber 301 shown in FIG. 12, a part of a piston rod 303 is inserted from above into a cylinder 302 in which oil is filled. A piston 304 is attached to the lower end portion of the piston rod 303. The piston 304 is slidably fitted in the up-down direction on the inner circumference of the cylinder 302. The inside of the cylinder 302 is sectioned into a cylinder upper chamber S11 and a cylinder lower chamber S12 by the piston 304.
The shock absorber 301 includes the damping force adjusting valve 310 connected via a hydraulic circuit including four check valves 305, 306, 307, and 308. The damping force adjusting valve 310 includes a slidable valve body 311, a valve seat 312 on which the valve body 311 is seated, and a spring 313 that urges the valve body 311 in a seating direction. The damping force can be adjusted by the single damping force adjusting valve 310 in both of a compression side stroke and an extension side stroke of the shock absorber 301.
That is, in the compression side stroke in which the piston 304 moves downward in the cylinder 302, the oil in the cylinder lower chamber S12 is compressed by the piston 304, and the pressure of the oil increases. The oil is supplied to the damping force adjusting valve 310 through the check valve 305 as indicated by solid line arrows in FIG. 12, whereby a compression side damping force is adjusted. The oil from the damping force adjusting valve 310 passes through the check valve 306 and flows into the cylinder upper chamber S11.
In the extension side stroke in which the piston 304 moves upward in the cylinder 302, the oil in the cylinder upper chamber S11 is compressed by the piston 304, and the pressure of the oil increases. The oil is supplied to the damping force adjusting valve 310 through the check valve 307 as indicated by broken line arrows in FIG. 12, whereby an extension side damping force is adjusted. The oil from the damping force adjusting valve 310 passes through the check valve 308 and flows into the cylinder lower chamber S12. Note that a capacity change in the cylinder 302 due to entry and exit of the piston rod 303 into and from the cylinder 302 in the compression side stroke and the extension side stroke is compensated by compression and expansion of gas in a reservoir 314.
However, in the shock absorber 201 shown in FIG. 11, the main disk valves 207 and 208 that respectively generate the compression side damping force and the extension side damping force and the back pressure chambers 213 and 214 for controlling the valve opening pressure of the main disk valves 207 and 208 are respectively provided. Therefore, the number of components increases, and the structure of the shock absorber 201 is complicated. A compact layout cannot be realized.
In the shock absorber 301 shown in FIG. 12, the single damping force adjusting valve 310 is used in common in both of the compression side stroke and the extension side stroke to adjust the damping force. However, arrangement for realizing a compact layout is not examined.